JPH064859B2 - Method for removing fine particles from coal liquefaction - Google Patents

Description

The present invention relates to the treatment of coal liquefaction products, and in particular to a method of removing fine particulate solids from liquefied coal.

Increasing coal utilization is interesting as a way to increase the supply of required energy. Development studies on the conversion of coal to produce clean liquids are supported by private enterprises and governments because the combustion of coal takes place in large stationary installations and is environmentally unfavorable due to high concentrations of sulfur and ash. It is based on.

In the direct conversion of coal, such as the solvent tefining of coal, the most difficult problem to deal with when obtaining a satisfactory coal liquefaction product is the problem of finely divided insoluble carbonaceous particles. The fine residual particles contained in the liquid product resulting from the liquefaction process and /
Or to remove other contained solid particulates therefrom. The ash content of the raw coal depends on the coal source, but is typically in the range of about 5-12% by weight. Although the particle size distribution of the fine particles from the coal liquefaction reactor is not clear, it is documented that the medium weight (mass median) particles have a diameter of 3 to 15 microns.

Various filters, centrifuges, hydrocyclones and the like are known in the art as means for removing fine solid particles from a dispersion system of a fluid medium. When removing solids from coal liquefaction products, with a centrifuge the centrifuge must be operated at low speeds throughout to achieve a satisfactory fining and is therefore uneconomical. On the contrary, the filter operation with the rotary drum pressure and the leaf filter are not controllable and the mechanical reliability is poor.

Hydrocyclones can provide liquid feeds with high solids concentrations, such as up to about 25% by weight.

However, these devices are not effective at removing solid particles of size less than about 5 microns.

Removal of dispersed solid particles from the fluidized medium is also accomplished by using an electrofilter. This electrofilter is effective in removing solid particles in the 0-10 micron range. However, these electrofilters cannot be used for feeds containing solid particles in amounts greater than about 5% by weight. A representative of the various electrofilters known in the art is US Pat.
3,770,605, 3,799,857, 3,928,158 and the patents cited therein.

A general object of the present invention is to provide a system and method for removing fine solid particles from a dispersion of a liquid medium. There, such solid contaminants are in the range of about 5-10% by weight and include 0-50 micron solid particles. More particularly, the present invention is suitable for removing ash or minerals containing solid particles from the coal liquefaction slurry feed. This feed is used in solvent coal refining, where solid contaminants contain ash and unconverted coal or carbon.

According to the invention, the removal of the solid contaminants contained in the liquefied coal is carried out by first centrifuging the coal liquefaction product as in a hydrocyclone to remove most of these solid contaminants. . The remaining ultrafine particles are then removed from the coal liquefaction product by electrofiltration. The ultrafine particles have particles in the range of up to about 5 microns and perhaps some particles up to about 10 microns. The combination of a hydrocyclone and an electrofilter to remove fine solid particle-containing ash from a coal liquefaction product of the type indicated has a complementary effect. These fine solid particles are made of _{(FeO, FeS, TiO 2,} Al 2 O 3, MgO, CaO, such as SiO _2, Na ₂ O and K ₂ O) inorganic and unconverted solid coal or carbonaceous material. Since particles are distributed according to their size,
Higher density component _{(FeO, FeS, TiO 2,} Al 2 O 3, MgO) is collected preferentially in a lower layer flow, therefore, the overflow portion includes particles finer than rich low density solid . By way of example, Table 1 shows the specific gravity of the fine solid particles produced from Kentucky # 9 coal at the Dotiki mine. Since unconverted coal has a lower density than any ash, the overflow is rich in unconverted carbon compared to the feed composition.

The removal of higher density components enhances the operation of the electrofilter. Fine solid particles of low conductivity (ie, high dielectric constant solids) reduce the ability of the electrofilter to store solids. According to the invention, these solid constituents of the high relative permittivity coal liquefaction products (Table 2) are also dense constituents. Therefore, it is selectively and preferentially removed by upstream hydrocyclone separation.

Table 2 Relative permittivity of fine solid particles of coal liquefaction product Compound relative permittivity FeO 14.20 TiO ₂ 86.00 Al ₂ O ₃ 9.34 MgO 9.70 CaO 11.80 SiO ₂ 4.50 Liquefied coal components Chrysene 3.46 Pyrene 3.80 Furthermore, electrofilter Is preferentially taken due to the difference in relative permittivity between solid and liquefied coal. Therefore, inorganics are preferentially removed and carbonaceous solids run off with coal liquefaction products. Since unconverted solid coal has a high BTU value, the fuel value increases when this substance is included in the coal liquefaction product.

The method of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a feed of liquefied coal slurry of the type used in solvent coal refining and containing dispersed solids is directed through line 10 to a first stage hydrocyclone system 11. Typically, some of this coal slurry has a boiling point above 850 ° F. In this first stage hydrocyclone system 11, separation occurs between a lower flow portion 12 having a higher solid content than the input and an overflow portion 13 having a lower solid content. In the first separation stage,
The ratio of the overflow portion to the lower layer flow portion is generally 0.8 to 1.2.
Is in the range. By appropriately adjusting the maximum removal of solids without limiting the lower stream discharge,
75-80% solids can be removed in this first hydrocyclone stage.

The first stage hydrocyclone system 11 and the second stage hydrocyclone system 14 described below can consist of a variety of hydrocyclones, as is well known in the art. For the purpose of this purpose, hydrocyclone system 11 and 1
4 can have a conventional structure as described in the following references: (1) "A Further Study of the Hydraulic
Cyclone, "Chemical Engineering Science (1953), Vol.
2, pp.254-272; (2) "A Theoretical Study of the Hydrau
lic Cyclone, "Industrial Chemist (1958, September), Vol.34, p
p.473-End; and (3) The TMC Dorr Clone-Aid to th
e Fluidized Catalytic Cracking Unit "Dorr Oliver In
Published by corporated (Print No. 4005).

The solid concentrate discharged from the first stage hydrocyclone through line 12 enters the second stage hydrocyclone system 14. There, further separation is carried out to obtain a second stage lower layer flow 15. This underflow 15 contains the majority of the initial fine solid particles of the initial feed that are charged through line 10.
Practically all of these particles are larger than about 5 microns. The overflow from the second stage hydrocyclone system discharged through line 16 is combined with the overflow from the first hydrocyclone stage in line 13. The combined overflow product is further subjected to separation treatment by electrofiltration.

The combined first and second stage overflows of lines 13 and 16 are introduced into the electrofilter system 17. The solids in this combined overflow are in the size range up to about 10 microns, predominantly 0-5 microns. This solid is preferentially incorporated into the inorganic matter because of its high density ash. The solids removed by the electrofilter contain ash preferentially because the dielectric constant of inorganic substances is higher than that of liquefied coal. Therefore, the uncollected solids contained in the electrofilter filtrate are mainly carbonaceous.

The electrofilter system 17 is, for example, US Pat.
Layered electrofilters (a bank o as described in 9,855, 3,799,857 and 3,928,158).
f electrofilters). The electrofilter is generally shaped like a cylindrical container 18 and is filled with monodisperse, uniform and smooth glass spheres 19. The diameter of the sphere is 1/16 to 1/2 inch,
It is preferably in the range of 1/8 to 1/4 inch. 10-50
A DC power source (not shown) of the KV supplies power to the central electrode or the multipolar electrode. The filter floor is grounded at a distance from the electrodes. Therefore, a voltage develops on this floor.

Fine particulate matter is collected on these spheres. When the solid amount corresponding to the floor capacity is reached, the power supply is stopped. And a suitable backwash liquid, preferably having a boiling point of about 300 ° F to
Coal-derived solvent in the range of about 850 ° F is passed through the bed by the means shown as 20. The amount of backwash liquid used is typically about two outflows from the bed (ie,
Equivalent to twice the amount of floor space). Duplex modules are used to obtain a nearly continuous flow. Therefore, even when one or more of the multiple electrofilters is in use, another electrofilter that has reached saturation can be subjected to backwash.

The filtered product is discharged via line 22 while the overflow confluent from lines 13 and 16 enters electrofilter bed 19. The filtrate recovered generally comprises about 80% or more of the initial feed fed to the system via line 10. Under properly selected operating conditions, the filtrate should contain less than about 0.1% finely divided solid particles.

The wash effluent is discharged via line 23 while the power supply is stopped and the floor 19 is backwashed. This wash effluent is
In fact it contains all the remaining fine solid particles. The solid particles have not been removed from line 15 by the second stage hydrocyclone system 14. They are mainly particles in the range 0 to 5 microns.

For the above system to work efficiently, it is necessary that the feed stream fed to the electrofilter contains no free water. Dissolved water must be below 1000ppm.

By operating the system shown in FIGS. 1 and 2, generally 95-99 +% by weight of the solids contained can be removed from coal liquefaction products having a feed agent concentration of 5-10% by weight. The liquid feed containing these solids has a flow rate (1.89-7.57 liters / min) between 0.5-2.0 gpm (gallons / min) / hydrocyclone under high temperature and high pressure in the first stage,
Preferably 1.0-1.5 gpm hydrocyclone flow rate (3.79-
5.68 liters / minute) is supplied to the layered hydrocyclone. The first stage hydrocyclone system 11 is tuned to maximize solids removal by allowing unlimited underflow discharge. The temperature of the supply liquid is adjusted so that the liquid viscosity is 10 cp or less, preferably 1 cp or less. In operation in the first hydrocyclone stage, the ratio of overflow to lower flow is
0.8-1.2, provided that removal of 75-80% solids can usually be expected. In the second stage hydrocyclone operation, the goal is to maximize the underflow concentration and minimize the loss of liquid product from the system. The overflow from the second stage can be combined with the overflow from the first stage (Fig. 1). However, the solid concentration in the combined overflow is approximately 3% by weight.
It is time to go down. Alternatively, the overflow from this second stage is recirculated and combined with the first stage feed when the concentration of the total combined fluid exceeds 3% by weight (Fig. 2).

To initially remove the fine solid particles from the coal liquefaction product, the coal product is fed to the first stage hydrocyclone system at a temperature such that its viscosity does not exceed about 3 cp.
The reason is that when the viscosity is higher than this, the separation efficiency is too low. The temperature is preferably 1c
It is selected so that the viscosity does not exceed p. This is about 600 ° F
Achieved at a temperature of (315 ° C).

There is no particular limitation on the pressure used in the operation of the hydrocyclone. However, the initial pressure level must be sufficiently above atmospheric pressure to have a pressure drop at each hydrocyclone stage and to prevent low boiling compounds from evaporating from the liquid. Pressure drop per stage is about 40-8
It is in the range of 0 psi (2.75 to 5.5 bars).

In the operation of an electrofilter, the temperature needs to be high enough so that the viscosity of the feed fed to this filter is less than about 10 cp. Furthermore, the temperature should be chosen so that the liquid resistivity is above 10 ⁸ cbm-cm. When the resistivity is low, the power consumption can be extremely high. Pressure is not a significant variable in electrofiltration. The pressure drop that would be required for an electrofilter of the type disclosed is on the order of about 15-30 psi (1-2 bars).

The system shown in FIG. 1 is particularly suitable for removing solids from coal liquefaction products having relatively low solids concentrations, such as those containing suspended solids not exceeding about 5% by weight. In order to obtain a relatively high solids feed, for example, as shown in Fig. 2, use a recirculation system with mutual stages between one hydrocyclone stage and another hydrocyclone stage. Is preferred.

FIG. 2 shows the same general apparatus as in the above embodiment. This equipment is the first stage hydrocyclone system 1
1, having a second stage hydrocyclone system 14 and an electrofilter system 17. Liquid coal is fed through line 30 to the inlet of the first stage hydrocyclone, line 3
It is separated into a lower layer flow portion discharged from 2 and an overflow portion discharged from the line 33. The underflow portion of line 32 is fed to the second stage hydrocyclone system 14 where it is split into the underflow portion of line 35 and the overflow portion of line 36. The underflow portion of line 35 actually contains all the fine solid particles sized above about 5 microns. This lower layer flow portion is discharged and used for downstream coke processing or gasification processing. The overflow portion of line 36 is recirculated and merged with the new feed of line 30. The overflow product resulting from the first stage hydrocyclone separation is sent to electrofilter 17 through line 33. In the electrofilter 17, remaining ultrafine solid particles are removed by depositing on the glass bead 19. As in the practical embodiment, power is supplied to the filter 17 while liquid is flowing into the filter and until the solid holding capacity of the floor 19 is at its limit.
When the capacity of the bed is reached, power is turned off and a suitable backwash liquid is passed through the bed. Therefore, the filtrate, which does not contain solids, is discharged from the filter 17 through line 42 while the liquid is flowing into the filter and operating. Backflushing liquid during the regeneration of floor 19
Be sent through. Then, the backwash effluent is discharged through the line 43.

The following Example 1 will be used to explain the actual operation when treating a coal liquefaction product having a total solids concentration of 5% or more using the flow apparatus of FIG.

Example 1 Each first and second stage hydrocyclone system (180-300)
It consists of a layered hydrocyclone. The diameter of the hydrocyclone is 10 mm. The feed is fed to a first stage hydrocyclone system. The temperature at this time is 500 ° F (260 ° C), the pressure is 200psi (1.38bars), and the flow rate is 1.2gpm (4.54 / min) per hydrocyclone. The feed liquid has a viscosity of 1.0 cp, a liquid density of 0.9 g / cm ³ and a solid density of 2.
It is 0 g / cm ³ . The size of the solid particles in the middle of the weight is 7.0 microns.

The overflow confluent in lines 13 and 16 is fed to the electrofilter system at 450 ° F (232 ° C).

Table 3 shows the flow distribution "F" and solids concentration. "F" equals the flow rate in the feed zone and "C" equals% solids by weight.

Under the conditions of Example 1, 80% of the solids were removed in the first hydrocyclone stage and 7% of the solids contained in line 12
5% is removed in the second stage. Electro filter 17
The incoming combined fluid has a solids content of 2.207% by weight, of which 96% solids are removed by subsequent electrofiltration.

Total solid removal is 98.4% and liquid recovery is 85.3% from the following equation.

Example 2 describes the procedure for treating a coal liquefaction product with a solids concentration of 8% by weight.

Example 2 The temperatures and pressures used are approximately in the ranges described in Example 1.

Table 4 shows the flow distribution and solid concentration.

% Separation efficiency stage solids removal in the first hydrocyclone 80 second hydrocyclone 75 electro filter 97 overall 99.25 present invention, typically, the solids concentration is sufficiently high (about 5 wt%
More than) and medium weight particles having a substantially large number of fine particles sized such that the diameter is about 10 microns or less.
However, the method of the present invention may be used to advantage in the treatment of other hydrocarbon liquids containing suspended solids which provide similar separation problems in terms of solids concentration and particle size distribution.

[Brief description of drawings]

FIG. 1 is a schematic flow diagram of an example of a system for separating dispersed solids from a liquid medium according to the present invention, and FIG. 2 is a schematic flow diagram of another embodiment. 11 ... First stage liquid cyclone system, 14 ... Second stage liquid cyclone system, 17 ... Electrofilter system, 19 ...
floor.

Claims (9)

[Claims] 1. A method for removing suspended fine solid particles contained in a coal liquefaction product, comprising: (a) subjecting the coal liquefaction product to a liquid cyclone treatment to fractionate the coal liquefaction product. A lower flow portion having a solids concentration substantially higher than that of the initial feed and an overflow portion having a lower solids concentration than the initial feed; said lower flow portion is made of FeO, FeS, TiO ₂ , Al. ₂ O ₃ , and at least one mineral selected from the group consisting of MgO, the overflow portion containing at least a majority of the particles of the initial feed ranging in size up to about 10 microns, (b) introducing the overflow portion into an electrostatic field of an electrofilter to deposit solids contained in the filter, (c) discharging the liquid filtrate containing no solids from the electrofilter, and (d) Liquid the electrofilter Periodically regenerating the filter by backwashing with flow to remove precipitated solids, and interrupting the supply of electrical energy to the filter during the backwashing step;
A coal-derived solvent having a boiling point in the range of 00 ° F to about 850 ° F. 2. The method of claim 1 wherein a portion of the coal liquefaction product has a boiling point above 850 ° F. 3. The hydrocyclone treatment is carried out in two stages, the underflow from the first stage is sent to the second stage; and the overflow from the second stage is the overflow from the first stage. A method as claimed in claim 1 in which the combined streams are combined and the combined overflows are sent to the electrostatic field of the electrofilter. 4. The hydrocyclone treatment is carried out in two stages, the underflow from the first stage is sent to the second stage, and the overflow from the second stage is the feed of the first stage. Claim 1 wherein the overflow from the first stage is recycled to the electrostatic field of the electrofilter.
The method described in the section. 5. A method according to claim 2 wherein the initial feed is subjected to a hydrocyclone treatment at a temperature such that the viscosity of the feed does not exceed 5 cp. 6. The method according to claim 2, wherein the initial feed is subjected to a hydrocyclone treatment at a temperature such that the viscosity of the feed does not exceed 1 cp. 7. The overflow product from the hydrocyclone treatment subjected to electrofiltration is at a temperature high enough to have a viscosity of 10 cp or less and at a liquid resistivity above 10 ⁸ ohm centimeters. A method according to claim 2 in claim 3. 8. A method according to claim 2 wherein said coal liquefaction product is obtained from a coal refining solvent process. 9. The coal liquefaction product has a medium weight particle size of about 7 microns, a solid density of about 2 g / cm ³ and a liquid density of about 0.9 g / cm ^3. The method of claim 2 wherein the method is subjected to a hydrocyclone treatment at a temperature of about 500 ° F and a pressure of 200 psi.